Multipath Mitigation Techniques for Satellite-Based Positioning Applications - Global Navigation Satellite Systems: Signal,Theory and Applications - page 413

(2003). technique offers better multipath rejection in medium-to-long delay multipath

in good C/N 0 Hurskainen et al. (2008); McGraw & Braasch (1999).

ΔΔ

Couple of well-known

particular cases of technique are the High Resolution Correlator (HRC) McGraw & Braasch

(1999), the Strobe Correlator (SC) Garin & Rousseau (1997); Irsigler & Eissfeller (2003), the
Pulse Aperture Correlator (PAC) Jones et al. (2004) and the modified correlator reference
waveform Irsigler & Eissfeller (2003); Weill (2003). One other similar tracking structure is
the Multiple Gate Delay (MGD) correlator Bello & Fante (2005); Bhuiyan (2006); Fante (2003;
2004); Jie (2010), where the number of early and late gates and the weighting factors used to
combine them in the discriminator are the parameters of the model, and can be optimized
according to the multipath profile as illustrated in Hurskainen et al. (2008); Jie (2010). While
coping better with the ambiguities of BOC correlation function, the MGD provides slightly
better performance than the nEML at the expense of higher complexity and is sensitive to
the parameters chosen in the discriminator function (i.e., weights, number of correlators and
correlator spacing) Bhuiyan (2006); Hurskainen et al. (2008); Jie (2010). In Hurskainen et al.
(2008), it is also shown that

ΔΔ

ΔΔ technique is a particular case of MGD implementation.

4.3 Early-late-slope

Another feedback tracking structure is the Early-Late-Slope (ELS) Irsigler & Eissfeller (2003),
which is also known as Multipath Elimination Technique (MET) Townsend & Fenton (1994).
The ELS is based on two correlator pairs at both sides of the correlation function's central
peak with parameterized spacing. Once both slopes are known, they can be used to compute
a pseudorange correction that can be applied to the pseudorange measurement. However,
simulation results performed in Irsigler & Eissfeller (2003) showed that ELS is outperformed
by HRC with respect to Multipath Error Envelopes (MEEs), for both BPSK and SinBOC(1,1)
modulated signals. An Improved ELS (IELS) technique was proposed by the Author in
Bhuiyan et al. (2008), which introduced two enhancements to the basic ELS approach. The
first enhancement was the adaptation of random spacing between the early and the late
correlator pairs, while the later one was the utilization of feedforward information in order
to determine the most appropriate peak on which the IELS technique should be applied. It
was shown in Bhuiyan et al. (2008) that IELS performed better than nEML only in good C/N 0
for BPSK and SinBOC(1,1) modulated signals in case of short-delay multipath, but still had
poorer performance than HRC.

4.4 A-Posteriori multipath estimation

A new multipath estimation technique, named as A-Posteriori Multipath Estimation (APME),
is proposed in Sleewaegen & Boon (2001), which relies on a-posteriori estimation of multipath
error. Multipath error is estimated independently in a multipath estimator module on the
basis of the correlation values from the prompt and very late correlators. The performance
of APME in multipath environment is comparable with that of the Strobe Correlator: a slight
improvement for very short delays (i.e., delays less than 20 meters), but rather significant
deterioration for medium delays Sleewaegen & Boon (2001).

4.5 Multipath estimating delay lock loop

One of the most promising state-of-art multipath mitigation techniques is the Multipath
Estimating Delay Lock Loop (MEDLL) Nee (1992); Nee et al. (1994); Townsend et al. (1995)